1. Field of the Invention
The present invention relates to a one-way clutch built-in type pulley apparatus for an alternator to be used in an automobile and a method for preventing an audible and annoying squeal of an endless belt for the alternator.
A one-way clutch built-in type driven pulley apparatus for an alternator and a method for preventing squeal of an endless belt for driving the alternator to be provided by the present invention is used for preventing a noise called squeal from occurring in an engagement portion between an endless belt for driving an alternator serving as the power generator of a car and a pulley on which this belt is wound.
2. Related Background Art
The structure of an alternator for generating an electric power necessary for a car by use of a running engine of the car serving as the driving source thereof as disclosed in, for example, Japanese Patent Laid-Open No. 7-139550. FIG. 8 shows the alternator 1 disclosed in this Laid-Open gazette. In the alternator 1, a rotary shaft 3 is rotatably supported by a pair of rolling bearings 4, 4 inside the housing 2. In a middle part of this rotary shaft 3, there are provided a rotor 5 and a commutator 6. Also, a driven pulley 7 is fixed to a portion projecting outward from the housing 2 at one end portion (the right end portion in FIG. 8) of this rotary shaft 3. In the state in which it is assembled in the engine, an endless belt is passed over or wrapped around from this driven pulley 7 to a driving pulley (not shown) which is fixed to an end portion of a crank shaft of the engine so as to allow rotation and driving of the rotary shaft 3.
Hitherto, as this pulley 7, a pulley which is simply fixed to the rotary shaft 3 is generally used. However, a variety of kinds of a one-way clutch built-in type driven pulley apparatus for an alternator are proposed recently, which allow transmission of the drive force from the endless belt to the rotary shaft when a running speed of the endless belt is fixed or shows an upward tendency, while allowing a relative rotation between the driven pulley and the rotary shaft when the running speed of the endless belt shows a downward tendency. Some of such pulley apparatuses are already used in practice. For example, a several kinds of such one-way clutch built-in type driven pulley apparatus for an alternator having a function as mentioned above are disclosed in Japanese Patent Laid-Open Nos. 56-101353, 7-317807, 8-61443, and 8-226462, and Patent Publication No. 7-72585, French Patent Publication No. FR2726059A1, etc.
Out of them, FIG. 9 shows the one-way clutch built-in type driven pulley apparatus for an alternator disclosed in Japanese Patent Laid-Open No. 8-226462. This one-way clutch built-in type driven pulley apparatus for an alternator has a sleeve 8 which is fitted on and fixed to the rotary shaft 3 of the alternator 1. Around this sleeve 8, a driven pulley 7a is provided concentrically with this sleeve 8. On the outer peripheral surface of this driven pulley 7a, there are formed a plurality of grooves 9, 9 (five in FIG. 9) each having V-shaped cross section and extending along the entire circumference in parallel to each other. An endless belt which is a V-ribbed belt for a car by Japanese Automobile Standards Organization (JASO) standard and has a plurality of ribs each having a V-shaped cross section and extending along the entire circumference on the inner peripheral surface thereof is passed over between such driven sleeve 7a and the unrepresented driving pulley. In this state, the ribs formed on the inner peripheral surface of this endless belt and the grooves 9, 9 are brought into a meshing state in a wedge-shaped manner, respectively, so that a surface pressure of a contact portion between the ribs and the grooves 9, 9 is securely fixed, whereby a large drive force (tractive force) can be transmitted between the endless belt and the driven pulley 7a.
A pair of support bearings 10, 10 and a roller clutch 11 are provided between the outer peripheral surface of the sleeve 8 and the inner peripheral surface of the driven pulley 7a. Out of them, the support bearings 10, 10 allow a relative rotation between the sleeve 8 and the driven pulley 7a, while supporting a radial load which is applied on the driven pulley 7a. The roller clutch 11 allows transmission of the rotating force from this driven pulley 7a to the sleeve 8 only when the driven pulley 7a is inclined to rotate relatively to the sleeve 8 in a given direction.
On the outer peripheral surface of the middle part of an inner race 12 which constitutes the roller clutch 11 and is fitted on and fixed to the sleeve 8, a plurality of recesses 13, 13 collectively called a ramp portion are formed at regular intervals in the circumferential direction, thereby making the outer peripheral surface of the middle part a cam surface 14. The outer peripheral surfaces of the both ends of the inner race 12 serve as inner race-ways 15, 15 for the support bearings 10, 10. On the other hand, the inner peripheral surface of the outer race 16 which constitutes the roller clutch 11 and is fitted in and fixed to the driven pulley 7a is formed as a simple cylindrical surface substantially over the entire length thereof. A plurality of rollers 17, 17 for constituting the roller clutch 11, together with the inner race 12 and an outer race 16, are supported by a clutch retainer 18 to be capable of rolling and displacing to some extent in the circumferential direction. Then, there is provided a spring between a column portion arranged in this clutch retainer 18 and each of the rollers 17, 17 so that the rollers 17, 17 are elastically pressed in the same direction with respect to the circumferential direction. Note that the structure and the function of the roller clutch 11 are conventionally known so that detailed illustration and description thereof will be omitted.
A roller clutch built-in type driven pulley apparatus for an alternator as mentioned above is conventionally installed onto the rotary shaft 3 of the alternator 1 (FIG. 8) for the following reason. That is, if, for example, the driving engine is a diesel engine, the angular velocity of rotation of the crank shaft fluctuates largely (for example, a rate of fluctuation becomes 20% or around) at the time of idling or low speed rotation. As a result, the running speed of the unrepresented endless belt which is wrapped over the driving pulley fixed to the end portion of the crank shaft also fluctuates finely. On the other hand, the rotary shaft 3 of the alternator 1 which is driven to rotate by this endless belt through the driven pulley 7a does not fluctuate so drastically owing to the inertial masses of this rotary shaft 3 and the rotor 5, the commutator 6 (FIG. 8) and the like fixed to this rotary shaft 3. Accordingly, when the driven pulley 7a is simply fixed with respect to the rotary shaft 3, the endless belt and the driven pulley 7a are inclined to rub against each other in the both directions upon a fluctuation in angular velocity of rotation of the crank shaft. As a result, stress in the different directions acts repeatedly on the endless belt which rubs against this driven pulley 7a, so as to cause easy slippage between this endless belt and the driven pulley 7a, or a deteriorated durability of the endless belt.
Deterioration of the durability of the endless belt based on the friction between the outer peripheral surface of the driven pulley 7a and the inner peripheral surface of the endless belt as described above is also caused by repeated acceleration and deceleration at running time. That is, the driving force is transmitted from the endless belt side to the driven pulley 7a side at acceleration, while the braking force is operated from the endless belt on the driven pulley 7a which tends to continuously rotate based on inertia, as described above, at deceleration. The braking force and the driving force respectively act as frictional forces in the opposite directions with respect to the inner peripheral surface of the endless belt, which also causes deterioration of the durability of the endless belt. Particularly, in case of a vehicle which is equipped with an exhaust brake such as a motor truck, deceleration of rotation of the crank shaft is conspicuous when the accelerator is off and the frictional force applied on the inner peripheral surface of the endless belt becomes large owing to the braking force. As a result, the durability of the endless belt is conspicuously deteriorated.
Then, by the use of the above-mentioned one-way clutch built-in type driven pulley apparatus for an alternator as the driven pulley 7a, it is arranged such that the rotating force is transmitted from the driven pulley 7a to the rotary shaft 3 when the running speed of the endless belt is fixed or has an upward tendency , while the driven pulley 7a and the rotary shaft 3 are rotated relative to each other when the running speed of the endless belt has a downward tendency. That is, when the running speed of the endless belt has a downward tendency, the angular velocity of rotation of the driven pulley 7a is set to be slower than that of the rotary shaft 3, thereby preventing the endless belt and the driven pulley 7a from rubbing against each other strongly at a contact portion therebetween. With such arrangement, the direction of a stress acting on the part at which the driven pulley 7a and the endless belt rub against each other is fixed so as to prevent slippage between this endless belt and the driven pulley 7a or deterioration of the durability of the endless belt.
As described above, the one-way clutch built-in type pulley apparatus is conventionally assembled in a driven pulley attached to an alternator, only aiming of prolonging the life of an endless belt which is used for driving. On the other hand, it is conventionally known that in such endless belt for driving the alternator a sound offensive to the ear called squeal is often generated owing to sliding friction at a contact portion between the belt and the driven pulley. In order to prevent such squeal, it is conventionally arranged that the diameter of the driven pulley is enlarged or the number of grooves on the outer peripheral surface of this driven pulley and the number of ribs on the inner peripheral surface of the endless belt are increased.
However, there is a limit to enlargement of the diameter of the driven pulley or increase of the number of the grooves or the ribs in terms of a space for installation. Moreover, if the diameter of the driven pulley is enlarged, the speed of rotation of the rotor of the alternator declines, so as to decrease the efficiency in power generation or cause other problems.